System for combined transcutaneous blood gas monitoring and negative pressure wound treatment

ABSTRACT

A system for administering negative pressure therapy to a wound includes a screen adapted to be positioned at the wound. A reduced pressure source is in fluid communication with the screen, and a blood gas transducer is exposed to a reduced pressure provided by the reduced pressure source. The reduced pressure supplied by the reduced pressure source induces hyperperfusion of a blood gas at the wound.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/867,990, filed Jun. 15, 2004, which is a continuation of U.S. patentapplication Ser. No. 10/085,321, filed Feb. 28, 2002, now U.S. Pat. No.6,856,821, which is a continuation-in-part of U.S. patent applicationSer. No. 09/579,755, filed May 26, 2000, now abandoned, which claims thebenefit of U.S. Provisional Application No. 60/136,293, filed May 27,1999. All of the above-referenced applications are hereby incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to the monitoring of blood gases duringvacuum assisted wound healing. More particularly, the invention relatesto a method and system for the transcutaneous monitoring of blood gaseswherein said monitoring is enhanced by application of a vacuum pressurein the region of skin under evaluation, and during which negativepressure therapy is being applied to an adjacent or proximal wound site.

BACKGROUND OF THE INVENTION

Transcutaneous blood gas monitoring is known in the relevant arts as amethod by which measurements of skin-surface gas pressures may beutilized to estimate arterial partial pressures of the gas of interest.In particular, skin surface oxygen or carbon dioxide pressure PO₂ orPCO₂, respectively, is measured by a locally applied, electrochemicallybased device in order to develop an estimate of arterial partialpressure of oxygen or carbon dioxide PaO₂ or PaCO₂, respectively. Theobtained estimate is then made available to the clinician as an aid forthe routine or emergency assessment of any of a variety of knowncardiopulmonary functions.

In practice, a condition of hyperperfusion is indicated in the region ofskin adjacent the applied device in order to enhance the flow ofarterial blood gases toward and through the skin surface. To date, thishyperperfusion condition has been established by local heating of theskin with an electrode in order to distend the arterial capillaries.Unfortunately, such local heating carries with it an increased risk fortissue injury—erythema, blisters, bums and skin tears being among thedocumented complications. In addition, some debate exists within the artas to whether the increased local metabolic rate concomitant theapplication of heat counteracts the intended perfusion effect. If so,false readings may result, which may ultimately lead to inappropriatetreatment of the patient.

The use of transcutaneous blood gas monitoring can be particularlyadvantageous when used in conjunction with negative pressure therapy forvacuum induced healing of open wounds or other tissue damage. Vacuuminduced healing of open wounds has recently been popularized by KineticConcepts, Inc. of San Antonio, Tex., by its commercially availableV.A.C.® product line. The vacuum induced healing process has beendescribed in commonly assigned U.S. Pat. No. 4,969,880 issued on Nov.13, 1990 to Zamierowski, as well as its continuations and continuationsin part, U.S. Pat. No. 5,100,396, issued on Mar. 31 1992, U.S. Pat. No.5,261,893, issued Nov. 16, 1993, and U.S. Pat. No. 5,527,293, issuedJun. 18, 1996, the disclosures of which are incorporated herein by thisreference. Further improvements and modifications of the vacuum inducedhealing process are also described in U.S. Pat. No. 6,071,267, issued onJun. 6, 2000 to Zamierowski and U.S. Pat. Nos. 5,636,643 and 5,645,081issued to Argenta et al. on Jun. 10, 1997 and July 8, 1997 respectively,the disclosures of which are incorporated by reference as though fullyset forth herein. Additional improvements have also been described inU.S. Pat. No. 6,142,982, issued on Nov. 7, 2000 to Hunt, et al.

The use of transcutaneous blood gas monitoring in conjunction withV.A.C.® therapy allows for monitoring of blood gases within and aroundthe wound bed. Blood gases can be an indicative factor of wound healingprogression. Crucial information can be ascertained as to theprogression of the wound without disturbing the wound dressing.

It is therefore a primary object of the present invention to improveover the prior art by providing a method and apparatus for thetranscutaneous monitoring of blood gases wherein local heating forhyperperfusion is eliminated, thereby eliminating a significant patienthazard and wherein the concomitant metabolic effects of local heatingare likewise eliminated, thereby reducing the likelihood formisdiagnosis leading to inappropriate treatment regimen.

Hyperperfusion through local heating also requires a prolonged warm upand stabilization time following electrode placement in order forequilibration and calibration of the electrochemical transducer. As aresult, operator time is generally wasted in the administration of atranscutaneous blood gas evaluation. Additionally, transcutaneous bloodgas monitors are either not available for emergency use or must be madeavailable with an operated in a standby mode. Such a standby moderequires additional hardware and generally shortens the electrodelifecycle.

It is therefore a further object of the present invention to improveover the prior art by providing a method and apparatus for thetranscutaneous monitoring of blood gases wherein the apparatus isavailable for full operation on short notice without requirement foradditional and/or lifecycle shortening hardware.

It is still a further object of the present invention to provide asystem and method that combines the advantages of a non-invasive bloodgas monitoring device with the effectiveness of negative pressuretherapy upon wounds, so as to further improve the efficacy of negativepressure therapy on the treatment of wounds and other tissue treatments.

Finally it is still a further object of the present invention to improveover the prior art by providing a method and apparatus for thetranscutaneous monitoring of blood gases wherein the above-describedobjects are implemented without sacrifice to patient safety or deviceefficacy, but wherein unnecessary hardware and software is nonethelessavoided, thereby conserving the ever more limited healthcare dollar.

SUMMARY OF THE INVENTION

In accordance with the foregoing objects, the present invention—a methodand system for the transcutaneous monitoring of blood gases and vacuumassisted wound closure—generally comprises a blood gas data acquisitiondevice, a vacuum source and a blood gas transducer unit. The blood gastransducer is adapted for application to a patient's skin andadministration of a local vacuum at the area of patient application. Itfurther comprises an electrochemical blood gas transducer, well known tothose of ordinary skill in the art, which is disposed entirely withinthe local vacuum at the area of patient application. The transducer mayalso be disposed within a wound site, or an area immediately adjacent awound site that is being treated by negative pressure therapy. The useof negative pressure therapy may include a porous, semi-rigid screenplaced within a wound bed, a cover for maintaining a negative pressurewithin the wound bed that is placed over the screen and wound bed, and avacuum source in fluid communication with the screen. Additionally, acanister may be disposed between the screen and vacuum source, for thecollection of fluids that may emanate from the wound during applicationof negative pressure by the vacuum source. A flexible tube or similardevice is used to communicate between the screen and vacuum source.

It is contemplated that the transducer may be incorporated within thescreen, or alternatively placed as a separate element below the screento be in direct contact with the wound bed, within a depression orcut-out of the screen, above the screen, or separate from the screen butimmediately adjacent the wound bed.

The blood gas transducer unit is in fluid communication with the vacuumsource through an interposed vacuum hose and in electrical communicationwith the blood gas data acquisition device through an interposedelectrical cable. The vacuum source, which comprises a vacuum pumpoperated by a pump motor is placed in fluid communication with the bloodgas transducer unit in order to induce a condition of hyperperfusion inthe locality of the electrochemical blood has transducer. Under thecontrol of the microcontroller, or equivalent means, the blood gas dataacquisition device is then utilized to capture this measure to arrive atan estimate of arterial partial pressure of oxygen or carbon dioxide,accordingly. Because vacuum induced perfusion produces the requisitecondition of hyperperfusion without local heating and, therefore,without acceleration of the local metabolic function, the presentinvention results in more accurate than previously available estimatesof partial blood gas pressures and does so while eliminating asignificant risk for injury to the patient.

The same vacuum source, or alternatively a second vacuum source, may beutilized to provide negative pressure at the wound site by communicatingwith the screen placed within the wound site, by means of a tube orsimilar device.

Because the application of vacuum perfusion to the patient presents atleast some risk for contamination of the vacuum source and blood gasdata acquisition device, the preferred embodiment of the presentinvention further comprises a transducer interface module particularlyadapted for the reduction or elimination of contamination risk.According to the invention, the transducer interface module comprises amale and female interface pair, wherein the male portion is adapted intothe female portion and thereby establishes communication between theblood gas transducer unit and the vacuum source and blood gas dataacquisition device.

In implementing the male plug, a hydrophobic membrane filter—known tothose of ordinary skill in the art—is interposed in the vacuum hose,thereby eliminating the opportunity for contaminants to pass from thepatient to the vacuum source or blood gas data acquisition device. Whilethe preferred embodiment of the present invention comprises a throw-awaymale plug, vacuum hose, electrical cable and blood gas transducer unit,those of ordinary skill in the art will recognize that each of thesecomponents can be made reusable with implementation of proper, knownsterilization techniques. In this latter case, the hydrophobic membranefilter is preferably replaceable.

Finally, many other features, objects and advantages of the presentinvention will be apparent to those of ordinary skill in the relevantarts, especially in light of the foregoing discussions and the followingdrawings and exemplary detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will now bedescribed with reference to the drawings of certain preferredembodiments, which are intended to illustrate and not to limit theinvention, and wherein like reference numbers refer to like components,and in which:

FIG. 1 shows, in perspective view, the preferred embodiment of thetranscutaneous blood gas monitoring apparatus of the present invention,as employed with a human subject;

FIG. 2 shows, in schematic block diagram, details of the apparatus ofFIG. 1; and

FIG. 3 shows, in schematic block diagram, a transcutaneous blood gasmonitoring device utilized in conjunction with a negative pressuretherapy device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although those of ordinary skill in the art will readily recognize manyalternative embodiments, especially in light of the illustrationsprovided herein, this detailed description is exemplary of the preferredembodiment of the present invention, the scope of which is limited onlyby the claims that may be drawn hereto.

Referring now to FIG. 1, the preferred embodiment of the transcutaneousblood gas monitoring system 10 of the present invention is shown togenerally comprise a blood gas data acquisition device 11, a vacuumsource 12 and a blood gas transducer unit 13. As shown in FIG. 1, theblood gas transducer unit 13 is adapted for application to a patient'sskin 14. In alternative embodiments, not shown, the blood gas transducermay be applied within a wound bed 30 or disposed within a screen 32placed within the wound bed 30. As will be better understood furtherherein, the blood gas transducer unit 13 is also adapted foradministration of a local vacuum at the area of the patient application.Finally, the blood gas transducer unit 13 comprises an electrochemicalblood gas transducer 15, well known to those of ordinary skill in theart, which is disposed entirely within the local vacuum at the area ofpatient application.

As also depicted in FIG. 1, the blood gas transducer unit 13 is in fluidcommunication with the vacuum source 12 through an interposed vacuumhose 16 and in electrical communication with the blood gas dataacquisition device 11 through an interposed electrical cable 17.Although those of ordinary skill in the art will recognize manysubstantial equivalents, the preferred embodiment of the presentinvention comprises a unitary hose and cable pair 18. Such a unitarypair 18 serves to reduce clutter in the patient care environment,thereby reducing the likelihood of either the hose 16 or cable 17becoming entangled with other tubes, cables or equipment. Further, andas will be better understood further herein, such a unitary pair 18 isespecially adapted for use with the preferred embodiment of the noveltransducer interface module 19 of the present invention.

According to the preferred embodiment of the present invention, thevacuum source 12 comprises a vacuum pump 20 operated by a pump motor 21.Those of ordinary skill in the art, however, will recognize manysubstantially equivalent embodiments for the vacuum source 12 including,for example, a central hospital vacuum or suction source or an integralpump and motor. In any case, all such equivalents are considered withinthe scope of the invention, which requires only a vacuum source 12 ofthe character otherwise described herein, and which is capable ofproviding suction in the range of about 50 mmHg through 250 mmHg.

In operation, the vacuum source 12 is placed in fluid communication withthe blood gas transducer unit 13 in order to induce a condition ofhyperperfusion in the locality of the electrochemical blood gastransducer 15. Under the control of a microcontroller 22, or equivalentmeans, the blood gas data acquisition device 11 is then utilized tocapture a measure of skin surface oxygen or carbon dioxide pressure. Themicrocontroller 22 can then utilize this measure to arrive at anestimate of arterial partial pressure of oxygen or carbon dioxide,accordingly. Because vacuum induced perfusion produces the requisitecondition of hyperperfusion without local heating and, therefore,without acceleration of the local metabolic function, the presentinvention results in more accurate than previously available estimatesof partial blood gas pressures and does so while eliminating asignificant risk for injury to the patient.

Because the application of vacuum to the patient presents at least somerisk for contamination of the vacuum source 12 and blood gas dataacquisition device 11, the preferred embodiment of the present inventionfurther comprises a transducer interface module 19 particularly adaptedfor the reduction or elimination of contamination risk. According to theinvention, the transducer interface module 19 comprises a male 23 andfemale 24 interface pair, wherein the male portion 23 is adapted to pluginto the female portion 24 and thereby establish communication betweenthe blood gas transducer unit 13 and the vacuum source 12 and blood gasacquisition device 11.

In implementing the male plug 23, a hydrophobic membrane filter 25—knownto those of ordinary skill in the art—is interposed in the vacuum hose16, thereby eliminating the opportunity for contaminants to pass fromthe patient 14 to the vacuum source 12 or blood gas data acquisitiondevice 11. While the preferred embodiment of the present inventioncomprises a throw-away male plug 23, vacuum hose 16, electrical cable 17and blood gas transducer unit 13, those of ordinary skill in the artwill recognize that each of these components can be made reusable withimplementation of proper, known sterilization techniques. In this lattercase, the hydrophobic membrane filter 25 is preferably replaceable.

Referring now to FIG. 3, a collection canister 34 may be interposedbetween the vacuum source 12 and the screen 32. As suction is applied,fluids may be drawn from the wound 30 and collected in the canister 34.A common vacuum source 12 may be utilized to provide vacuum perfusion tothe blood gas transducer 13 and negative pressure to the wound site 30.A seal 36 is adhered over the screen 32 in order to maintain negativepressure within the wound site 30. The seal 36 may be comprised of anelastomeric material. The screen 32 is preferably comprised ofpoly-vinyl alcohol foam, or alternatively a polyurethane porous sheet.It is to be understood that any semi-rigid and porous material may beutilized as a screen 32 within the wound bed 30. The tube 16 may be indirect fluid communication with the screen 32 (not shown), or connectedto an adapter 38 that is adhered over an opening 40 in the seal 36. Itis preferable that the tube 16 is bifurcated at a position between thevacuum source 12 and the canister 34 so that fluids being drawn from thewound site 30 do not interfere with the vacuum perfusion of the bloodgas transducer 13.

In an alternate embodiment, not shown, a separate vacuum source may beutilized to provide negative pressure to the wound site 30 and anothervacuum source utilized to provide vacuum perfusion to the blood gastransducer 13.

While the foregoing description is exemplary of the preferred embodimentof the present invention, those of ordinary skill in the relevant artswill recognize the many variations, alterations, modifications,substitutions and the like as are readily possible, especially in lightof this description and the accompanying drawings. For example, amembrane or other like switch pad 26 may be implemented for user controlof the transcutaneous blood gas monitor 10 and/or a display, printer orother output device 27 may be provided for monitoring and/ or recordingof estimated partial pressures. Likewise, a pressure transducer 28 maybe, and preferably is, provided for monitoring and control of the vacuumapplied to the patient 14. In any case, because the scope of the presentinvention is much broader than any particular embodiment,, the foregoingdetailed description should not be construed as a limitation of thescope of the present invention, which is limited only by the claims thatmay be drawn hereto.

1. A system for administering negative pressure therapy to a wound, thesystem comprising: a screen adapted to be positioned at the wound; areduced pressure source in fluid communication with the screen; a bloodgas transducer exposed to a reduced pressure provided by the reducedpressure source; and wherein the reduced pressure supplied by thereduced pressure source induces hyperperfusion of a blood gas at thewound.
 2. The system of claim 1, wherein the blood gas transducer is anelectrochemical blood gas transducer.
 3. The system of claim 1, furthercomprising: a cover adapted to be positioned over the screen at thewound to maintain the reduced pressure at the wound; and wherein theblood gas transducer is adapted to be positioned beneath the cover. 4.The system of claim 1, further comprising: a blood gas data acquisitiondevice in communication with the blood gas transducer to capture ameasure of gas pressure of the blood gas.
 5. The system of claim 4,wherein the blood gas data acquisition device is further capable ofestimating an arterial partial pressure of the blood gas using themeasured gas pressure.
 6. The system of claim 4, wherein the blood gasis oxygen.
 7. The system of claim 4, wherein the blood gas is carbondioxide.
 8. The system of claim 4, wherein the blood gas transducer iselectrically connected to the blood gas data acquisition device by anelectrical cable.
 9. The system of claim 8, wherein the reduced pressuresource is in fluid communication with the blood gas transducer via ahose, the hose and electrical cable forming a unitary hose and cablepair.
 10. The system of claim 1, further comprising: a hydrophobicmembrane positioned between the blood gas transducer and the reducedpressure source.
 11. The system of claim 4, further comprising: atransducer interface module operable to provide fluid communicationbetween the reduced pressure source and the blood gas transducer, thetransducer interface module further operable to provide electricalcommunication between the blood gas data acquisition device and theblood gas transducer.
 12. The system of claim 11, wherein the transducerinterface module comprises a male and female interference pair.
 13. Thesystem of claim 12, further comprising: a hydrophobic membrane filterdisposed in a male portion of the male and female interference pair. 14.The system of claim 1, wherein the blood gas transducer is at leastpartially disposed in the screen.
 15. The system of claim 1, wherein thescreen is a porous foam.
 16. A transcutaneous blood gas monitoringsystem comprising: a blood gas transducer unit adapted to be disposedadjacent a tissue site, the blood gas transducer unit having anelectrochemical blood gas transducer; a reduced pressure source in fluidcommunication with the blood gas transducer unit to expose the tissuesite and the electrochemical blood gas transducer to a reduced pressureto induce hyperperfusion of a blood gas at the tissue site; and a bloodgas data acquisition device in communication with the blood gastransducer unit to capture a measure of gas pressure of the blood gas toestimate an arterial partial pressure of the blood gas.
 17. The systemof claim 16, wherein the blood gas is oxygen.
 18. The system of claim16, wherein the blood gas is carbon dioxide.
 19. The system according toclaim 16 further comprising a hydrophobic membrane filter positionedbetween the blood gas transducer unit and the reduced pressure source.20. The system according to claim 16, wherein the tissue site is intactskin.
 21. The system according to claim 16, wherein the tissue site is awound undergoing negative pressure therapy.
 22. A method for monitoringa blood gas pressure comprising: inducing hyperperfusion of a blood gasat a tissue site by exposing the tissue site to a reduced pressure;measuring a gas pressure of the blood gas at the tissue site; andestimating an arterial partial pressure of the blood gas using themeasured gas pressure.
 23. The method of claim 22, wherein inducinghyperperfusion further comprises: applying a blood gas transducer unitto the tissue site; fluidly connecting a reduced pressure source to theblood gas transducer unit; and applying the reduced pressure to thetissue site via the blood gas transducer unit.
 24. The method of claim23, wherein the blood gas transducer unit includes an electrochemicalblood gas transducer.
 25. The method of claim 22, wherein the tissuesite is a skin surface.
 26. The method of claim 22, wherein the bloodgas is at least one of oxygen and carbon dioxide.